1. Field of the Invention
The present invention relates to a head position control method for a disk device, a head position control device, and a disk device, and more particularly to a head position control method, head position control device and disk device for suppressing position deviation due to external vibration and eccentricity of the disk.
2. Description of the Related Art
It is extremely important for a disk device, such as a magnetic disk device or optical disk device, to accurately position the head on the target track of the disk in order to improve recording density.
For this positioning control, various factors interrupt positioning accuracy of the head with respect to the disk. The eccentricity of the disk, in particular, causes a deterioration of position accuracy of the head. In order to control follow up of the head to the eccentricity of the disk, an eccentricity correction method using an eccentricity estimation observer has been proposed (e.g. Japanese Patent Application Laid-Open No. H7-50075 or Japanese Patent Application Laid-Open No. 2000-21104).
Such an eccentricity estimation observer calculates a control value of an actuator from an error between an actual position error and an estimated position error, using the state estimation gains A, B, C, F and L, and calculates the state quantities (position, velocity, bias value, eccentricity) of the next sample.
Here the estimated gain L consists of an estimated position gain L1, estimated velocity gain L2 and estimated bias gain L3, and estimated eccentricity gains L4 and L5. And L1, L2 and L3 show the characteristics of the controller itself, and L4 and L5 show the response characteristics to eccentricity, which is a periodic disturbance.